You must set this parameter for every instance, and multiple instances must have the same value.

DB_RECOVERY_FILE_DEST_SIZE specifies (in bytes) the hard limit on the total space to be used by target database recovery files created in the flash recovery area.

Note that neither block 0 nor the OS block header of each Oracle file is included in this size. Allow an extra 10% for this data when computing the actual disk usage required for the flash recovery area.